Method for diagnosing malfunctions in internal combustion engines

ABSTRACT

A method for diagnosing mechanical malfunctions of internal combustion engines resulting in unnecessarily high emissions of carbon monoxide and/or hydrocarbon is disclosed. The method comprises analyzing engine exhaust gases for carbon monoxide and hydrocarbon content while the engine is operated at both the idle and power carburetion circuits and comparing the analytical results obtained.

I United States Patent 91 [111 3,864,964

Voelz 1 Feb. 11, 1975 METHOD FOR DIAGNOSING 3,284,165 11/1966 Baumann eta1 73 23 x MALFUNCTIONS 1 INTERNAL 3,406,562 10/1968 Perna, Jr. et a1.73/1 16 X 3,407,646 10/1968 Traver 73/23 COMBUSTION ENGINES 3.427.8742/1969 Munroe et a1. 73/116 [75] Inventor; Frederick L. Voelz, OrlandPark, Ill, 3.472,()67 10/1969 Chew 73/116 [73] Assignee: AtlanticRichfield Company, New

York, Primary Examiner-Jerry W. Myracle [22] Fl d N 23 1970 Attorney,Agent, or Firm-Frank J. Uxa

ie 0v.

[21] Appl. No.: 92,229 [57] ABSTRACT A method for diagnosing mechanicalmalfunctions of internal combustion engines resulting in unnecessarily[58] 2 I 18 high emissions of carbon monoxide and/or hydrocarle 0 carebon is disclosed. The method comprises analyzing engine exhaust gasesfor carbon monoxide and hydrocar- [56] References cued bon content whilethe engine is operated at both the UNITED STATES PATENTS idle and powercarburetion circuits and comparing the 2,597,231 5/1952 Edelen 73/118 UXanalytical results obtained. 3,211,534 10/1965 Ridgway 23/288 F X3,248,872 5/1966 Morrell 23/288 F X 10 Claims, N0 Drawings METHOD FORDIAGNOSING MALFUNCTIONS IN INTERNAL COMBUSTION ENGINES This inventionrelates to a method for reducing air pollution from internal combustionengines. More particularly, this invention relates to a method fordiagnosing mechanical malfunctions which can exist in internalcombustion engines and which can result in unnecessarily large amountsof carbon monoxide and hydrocarbons in the engine exhaust gases.

The internal combustion engine is used to power, among other things,practically all the transportation vehicles in use today. For example,this type of power system is used in 90 million automobiles in theUnited States alone. With the automobile population continuallyincreasing, the problem of diagnosing and correcting mechanicalmalfunctions of internal combustion engines in order to maintain each ofthese vehicles at maximum operating efficiency is becoming more and moredifficult. This problem is accentuated by the limited supply of trainedmechanics and technicians. Many of the techniques used to diagnoseengine malfunctions are expensive, cumbersome and time-consuming whichfurther limits the number of malfunctions which canbe properlydiagnosed, as well as inconveniencing the auto owner to the point wherehe may actually avoid having engine malfunctions diagnosed andcorrected.

The internal combustion engine manufactures useful power by theexplosive combustion of fuel, normally of the hydrocarbon type, such asnatural gas, gasoline, kerosene, diesel fuel, etc., and oxygen, normallytaken from air. It is almost inherent that a certain amount of carbonmonoxide and hydrocarbon will be present in the exhaust gases from theseengines. The carbon monoxide and hydrocarbons emitted from internalcombustion engines add significantly'to the overall problem of airpollution. Therefore, it would be advantageous to minimize the amountsof these harmful pollutants emitted in the exhausts of internalcombustion engines.

One method of reducing these harmful emissions is by properlymaintaining the internal combustion engine. A mechanicallymalfunctioning engine gives off substantially increased amounts ofcarbon monoxide and hydrocarbons. However, because of the previouslynoted complexity of current diagnostic techniques, many enginemalfunctions remain uncorrected and a potential substantial reduction inair pollution is not attained.

Various procedures for testing exhaust emissions from internalcombustion engines are known to the art. Many of these procedures may beused as diagnostic tools to pinpoint engine malfunctions. However, eachof these techniques are of limited use in the routine maintenancesurveillance of motor vehicle engines because such techniques can beunduly expensive, cumbersome and/or timeconsuming.

The most comprehensive of these emissions testing procedures is commonlyreferred to as the California Cycle and involve operating the enginebeing tested at idle and at six conditions using a chassis dynamometerto simulate actual road loading. Not only is the chassis dynamometer anexpensive piece of equipment, but it also is complex, requiringsubstantial time and a skilled technician to operate it properly. TheCalifornia Cycle involves analyzing the engine exhaust gas for variouscomponents (such as carbon monoxide and hydrocarbons) at each of theseven operating conditions. These individual emission values aremultiplied by weighting factors, which adjust the emission value by thetime normally spent operating the engine at the particular condition,and added together to give an overall emission profile for the engine.The table below gives the seven engine operating conditions and thecorresponding weighting factors for the California Cycle.

Using arbitrarily set standards for carbon monoxide and hydrocarbonemissions, it can be determined by operating an engine through theCalifornia Cycle whether the engine emits unacceptably large amounts ofcontaminants. However, since the California Cycle is a time-consumingand involved procedure requiring seven sets of analyses and the use of achassis dynamometer, routine emmisions surveillance of the approximatelymillion automobile engines presently in use in the United States isimpractical using this procedure. Furthermore, the primary purpose ofthe California Cycle is to determine the level of emissions and not whatthe causes of excessive emissions might be. Therefore, the usefulness ofthe California Cycle as a diagnostic tool is very much limited.

Cline and Tinkham have disclosed one method by whichmechanicalmalfunctions which result from excessively high carbonmonoxide and'hydrocarbon emissions can be diagnosed. See: A RealisticVehicle Emission Inspection System, Journal of the Air PollutionAssociation, 19, 230, 1969. This method involves analyzing engineexhaust gases for carbon monoxide and hydrocarbon content whileoperating the internal combustion engine of a motor vehicle at idle, andalso at low cruise and high cruise under load conditions, obtained usinga chassis dynamometer. The Cline Tinkham method sets arbitrarylimitations on the amounts of both carbon monoxide and hydrocarbonemissions permitted. If the engine emits more carbon monoxide than isacceptably permitted at any of the three operating levels, an overlyrich (i.e., high fuel) air-fuel mixture is indicated. If, on the otherhand, the amount of hydrocarbon emitted exceeds the arbitrary amountpermitted at any one of the three points of the Cline Tinkham cycle,fuel is escaping from at least one of the combustion chambers of theengine into the exhaust system without having been properly subjected tocombustion Although the Cline Tinkham method requires fewer exhaust gasanalyses than the California Cycle, it does have a number ofdisadvantages. In particular, like the California Cycle, the ClineTinkham method requires the use of a chassis dynamometer to provide theload conditions during testing and therefore, it burdened with many ofthe above noted disadvantages inherent in the California Cycle. Also,the Cline Tinkham procedure places total reliance upon arbitrarily setlevels of carbon monoxide and hydrocarbon engine emissions. This totalreliance may lead to unsound or, at

best, incomplete results. For example, the Cline Tinkham procedure maydetermine that a particular internal combustion engine is a non-highemitter since it fails to emit either carbon monoxide or hydrocarbons ata level greater than arbitrarily set for testing, and still the enginemay be emitting these harmful gases in amounts much above the minimumpossible. Such an engine would be declared a completely acceptableemitter by the Cline Tinkham method and still may be producingunnecessarily large amounts of carbon monoxide and hydrocarbons.Substantial reduction in the amount of carbon monoxide and/orhydrocarbon emitted might be realized if certain mechanical malfunctionsexisting in this non-high emitting" engine were corrected.

As is apparent from the foregoing, there is a need for a procedure whichcan be used to simply, inexpensively and quickly diagnose malfunctionsthat can exist in internal combustion engines to cause the emission ofunnecessarily large amounts of carbon monoxide and/or hydrocarbons inthe engine exhaust gases.

It has now been discovered that mechanical malfunctions of internalcombustion engines which cause unnecessarily high carbon monoxide and/orhydrocarbon exhaust gas emissions can be diagnosed by analyzing theexhaust gases from an internal combustion engine operated at only twoengine speeds without using a load simulating device, such as a chassisdynamometer. The exhaust gases to be analyzed for carbon monoxide andhydrocarbon content are sampled while the engine is being operated at:(I) idle, i.e., while the engine is being operated on the idlecarburetion circuit; and (2) a speed on the main carburetion circuit ofthe engine.

Therefore, in one aspect, the present invention is a method fordiagnosing malfunctions of internal combustion engines which result inexhaust gases having unnecessarily high concentrations of carbonmonoxide and hydrocarbons comprising:

(l) analyzing for the carbon monoxide and hydrocarbon concentrations ofthe exhaust gases from the engine sampled while the engine is beingoperated in modes (A) and (B), the two engine operational modes being atessentially constant no load conditions at normal operating temperaturesand (A) on the idle carburetion circuit and (B) on the main carburetioncircuit, the engine being operated in modes (A) and (B) in anychronological sequence; and

2. comparing at least one of said carbon monoxide and hydrocarbonconcentrations, wherein engine malfunctions resulting in an overly richair-fuel mixture to the engine are indicated when the carbon monoxideconcentration obtained from operational mode (B) exceeds that fromoperational mode (A), and engine malfunctions resulting in improper fuelcombustion are indicated when the hydrocarbon concentration obtainedfrom operational mode (B) exceeds that from operational mode (A).

In order to practice the present invention, it is necessary to operatethe engine at only two speeds. One speed is idle, i.e., the engine isoperated on the idle carburetion circuit. The other engine speed is onthe main carburetion circuit, rather than the idle circuit. Idlecarburetion circuit operation is normally achieved at engine speeds fromabout 400 rpm. to about 1 I rpm. For many internal combustion engines,in particular engines of motor vehicles, i.e., automobiles, trucks,

etc., main carburetion circuit operation can be achieved by running theengine at a speed of at least about 1200 rpm. In order to insure thatthe engine is off the idle and on to the main circuit, it is preferredthat engine speeds of at least about 2000 rpm. be used. For safetyreasons, it is normally preferred not to exceed about 4000 rpm., morepreferably about 3000 rpm.. when practicing the method of thisinvention. Therefore, the preferred range of main circuit engine speedsis from about 1200 rpm. to about 4000 rpm., while the more preferredrange is from about 2000 rpm. to about 3000 rpm.

While testing the engine at idle and main carburetion circuit speeds,the engine is operated under no load conditions. The no load conditionmeans that the engine is essentially freerunning, i.e., not workingagainst a load whether real or simulated. Therefore, the presentinvention is practiced without expensive and complex load-simulatingequipment (e.g., chassis dynamometer). This no-load feature of thepresent invention provides a major advantage over prior art procedures.The present procedure is less expensive, quicker and requires less skillto practice than do the prior art procedures. The present inventionpermits the skilled technician or mechanic to devote the time andexpertise that had been spent setting up and running loaded engine teststo more difficult maintenance problems. This no-load feature also allowsmore engines to be tested in a given period of time, thus extending thepollution control benefits of the present invention to more motorists.This in turn, increases the overall pollution control benefits of theinvention.

In order to practice the present invention, it is not necessary to setany emission standards. It has been discovered that engine malfunctionswhich result in unnecessarily large amounts of harmful emissions can bediagnosed by comparing the carbon monoxide and/or hydrocarbon emissionsdata from idle and main carburetion circuit engine operation withoutregard to the absolute concentration of either contaminant. Thisdiscovery represents a major advance over the prior art procedures whichrelied entirely on arbitrarily set standards of exhaust gas carbonmonoxide and hydrocarbon concentration. By correcting mechanicalmalfunctions indicated by practicing the present invention, one mayreduce the exhuast gas concentration of carbon monoxide and hydrocarbonsto the minimum possible, rather than merely below some arbitrarily setstandard concentration. This enhances the pollution control benefits ofthe present invention in that diagnosis of mechanical malfunctions whichmay result in reductions in exhaust gas carbon monoxide and/orhydrocarbon concentration may be possible even though the initialconcentrations of these pollutants are below a previously set acceptablelevel.

Among the engine malfunctions resulting in an overly rich air-fuelmixture to the engine which can be indicated by practicing the presentinvention are the following: (l) improper carburetor adjustment; (2)restricting carburetor air filter element (i.e., the air filter elementis partially plugged, thereby impeding the flow of needed combustionair); (3) engine choke system not functioning properly; (4) malfunctionpositive crankcase ventilation system; and the like. Among the enginemalfunctions resulting in improper fuel combustion which can beindicated by practicing the present invention are the following; (1)engine ignition system malfunctions; (2) engine valve malfunctions; (3)worn or fouled spark plugs; (4) defective spark plug wire leads; (5)worn or defective piston rings; and the like. Once the method of thepresent invention has indicated the presence of an engine malfunction,further tests and procedures on individual components of the engine canbe used to pinpoint and/or correct the malfunction.

For example, if the method of the present invention indicates that anengine has a malfunction resulting in an overly rich air-fuel mixture,the carburetor air-filter element can be tested by the method disclosedin (Method by Frederick L. Voelz, Docket No. 13-0014, patent applicationSer. No. 82864 now Pat. No. 3,663,81 l) to determine if it isrestricting the flow of combustion air, and/or the engine carburetor canbe adjusted by the method disclosed in(Method" by Frederick L. Voelz,Docket No. 13-0015) to minimize the amounts of carbon monoxide andhydrocarbons emitted from the engine. Similarily, if the method of thepresent invention indicates that the engine has a malfunction resultingin improper combustion of fuel, various tests of the ignition system andcombustion chambers, for example, conventional inspection methods forspark plugs and spark plug leads, can serve to pinpoint themalfunctions.

Any internal combustion engine which can be run on both idle and maincarburetion circuits may be tested by the method of the presentinvention. Among the types of engines included are 2 cycle engines, 4cycle engines, rotary piston driven engines, turbine engines and thelike. Engines which are normally operated in association withtransportation means such as automobiles, trucks, etc., as well as thoseoperated in association with non-transportation means may be tested inthe practice of the present invention. Because of emission controlsystem revisions, certain (e.g. Ford Motor Company products) 1969 andall subsequent motor vehicle engines are somewhat insensitive to thataspect of the present invention which indicates malfunctions resultingin an overly rich air-fuel mixture. Severe engine malfunctions whichproduce an overly-rich air-fuel mixture in these engines may bediagnosed by the method of the present invention. The aspect of theinvention in which malfunctions resulting in improper fuel combustioncan be diagnosed is unaffected by the above-noted design changes.

In the method of the present invention, the engine is run at normaloperating temperatures to insure consistant results. In order to achievenormal operating temperatures, the engine may be run for a sufficientlylong time so that the engine choke system, if any, is completely openand does not itself restrict the flow of combustion air. In any case,normal engine operating temperatures vary depending on the type ofengine, air-fuel ratio, thermostating, etc. Generally, normal operatingtemperatures for internal combustion engines are from about 170 to about240F. (engine block temperature.)

The carbon monoxide and hydrocarbon contents of the exhaust gases may beanalyzed in any conventional manner known to the art. Included amongthese conventional analytical methods are gas chromatography, massspectrometry and infra-red spectrometry. Because of the speed andaccuracy of analysis, it is preferred to utilize infra-red spectrometryin the practice of the present invention. In particular, the use ofnondispersive infra-red (NDlR) analyzers is preferred in the practice ofthis invention. These infra-red analyzers operate on the known principlethat carbon monoxide gas and hydrocarbon gas absorb infra-red energyhaving specific wave lengths. When infra-red energy is sent through astream of engine exhaust gas, a certain amount of energy is absorbed bythe carbon monoxide (or hydrocarbons) in the gas stream. The amount ofabsorbed energy has a direct relationship to the volume concentration ofcarbon monoxide (or hydrocarbons) in the exhaust gas. By comparing,normally using electronic means, the amount of infra-red energy of thespecific wave length absorbed by carbon monoxide (or hydrocarbons)remaining with the original amount of infra-red energy of this wavelength, it is possible to determine the amount of carbon monoxide (orhydrocarbons) in the exhaust gas. This type of infra-red analyzer can bepackaged as a relatively portable and inexpensive instrument. Theanalyzer mobility and low cost are additional reasons for preferringinfra-red spectrometry for analyzing the carbon monoxide and hydrocarbonconcentrations of engine exhaust gases.

When testing internal combustion engines that are associated withautomobile and other motor vehicles, it is preferred to sample theengine exhaust gases for analysis from the tail pipe effluent, i.., theexhaust system effluent. Although it is not critical to the presentinvention which engine operational mode is run first, if the exhaustgases for analysis are sampled from the exhaust system effluent, it ispreferred to run the engine in mode (B) (main carburetion circuitoperation) prior to mode (A) (idle circuit operation). This procedure ispreferred since operating the engine on the main carburetion circuitclears the engine exhaust system and helps to insure representativesampling of the exhaust gases when the engine is operated at idle. lfoperational mode (A) is run prior to operational mode (B), it ispreferred that the engine be operated at an elevated speed (eg about2000 rpm.) for about 30 seconds to clear the engine exhaust system priorto operating the engine in mode (A).

Since the engine exhaust system (i.e., muffler, tail pipe, etc.,) issubject to great wear, the possibility of gas leaks exists. Therefore,in order to insure the accuracy and reproducibility of the tail pipeeffluent carbon monoxide and hydrocarbon analyses, it is preferred thatif the tail pipe effluent is used as the source for exhaust gas samples,the engine exhaust system be tested for gas leaks at some point duringthe practice of this invention. The point at which the leak testingtakes place is not critical to the present invention, although, forconvenience and time saving reasons, it is preferred that the leaktesting occur at or prior to the time of the first carbon monoxide andhydrocarbon analyses.

The exhaust system leak testing can be accomplished in any conventionalmanner, for example, visual inspection of the exhaust system. However,the preferred method of leak testing is to analyze the tail pipeeffluent for oxygen concentration. It is well known that the exhaustgases from a conventional four cycle internal combustion engine (thestandard automobile engine) operated on the idle carburetion circuitcontain between about l% to about 4% by volume of oxygen. Anysignificant deviation, for example, at least about 3% by volume from theupper limit of the above oxygen concentration range found in the tailpipe effluent indicates a leak in the engine exhaust system. Exhaustfrom engines which are equipped with air injection emission controldevices normally contain between about 7% to about 20% by volume ofoxygen, and therefore, may be deemed insensitive to the oxygen analysis"method for testing for air leaks. The oxygen concentration can beobtained by any conventional analytical method, such as amperometricmethods, magnetic susceptibility methods, gas chromatography and massspectrometry. The preferred methods of oxygen analysis are theamperometric methods.

The following examples illustrate more clearly the method of the presentinvention. However, these illustrations are not to be interpreted asspecific limitations on this invention.

EXAMPLE 1 A 1964 Pontiac automobile powered by a standard 4 cycle,internal combustion engine was selected for testing. During the test,the engine was run at no load conditions and at normal operatingtemperatures so that the engine choke system did not restrict the flowof combustion air. It was determined that the engine exhaust system wasin tact and that, therefore, reliable specimens of exhaust gas could beobtained by sampling the tail pipe effluent. The engine speed wasbrought to and maintained at 2500 rpm. (main carburetion circuitoperation) through the use of a portable tachometer. While maintainingthe speed of the engine at 2500 rpm., the exhaust gases (tail pipeeffluent) from the engine were analyzed for carbon monoxide andhydrocarbon concentrations by means of a portable non-dispersiveinfra-red analyzer. The carbon monoxide concentration was determined tobe 3.75% by volume of the total exhaust gases, and the hydrocarbonconcentration was determined to be 380 ppm.

The engine speed was then reduced to idle, about 440 rpm., and theexhaust gases were again analyzed for carbon monoxide and hydrocarbonconcentration. At this point, the exhaust gases contained 1.3% by volumecarbon monoxide and 440 ppm. hydrocarbon.

These analytical data indicated that the engine was receiving anoverly-rich air-fuel mixture. It was determined, using the method of(Method by Frederick L. Voelz, Docket No. 13-0014, patent applicationSer. No. 82864 now patent no. 3,663,811), that the carburetor air filterelement was restricting the flow of combustion air to the engine. Theused carburetor air filter element was replaced by a non-restrictingelement. This maintenance procedure resulted in an exhaust gas carbonmonoxide concentration reduction of 20% at 2500 rpm. and about 4% at theidle carburetion circuit operation.

EXAMPLE 2 A 1968 Chevrolet automobile equipped with a standard 4 cycle,internal combustion engine was tested in a manner similar to that ofExample 1. The carbon monoxide concentration of the exhaust gases at2500 rpm. was determined to be 1.0% by volume while the concentration atidle carburetion circuit operation was 0.4% by volume. Exhaust gashydrocarbon concentration at 2500 rpm. was 80 ppm. and at idle was 180ppm. These data indicated that the engine was receiving an overly richair-fuel mixture.

Various engine components were tested including the positive crankcaseventilation system. The positive crankcase ventilation system waspressure tested and determined to be operating at less vacuum thandesirable. Therefore, the positive crankcase ventilation valve wasreplaced. This maintenance procedure resulted in an exhaust gas carbonmonoxide concentration reduction of 30% at 2500 rpm. and 50% at idlecircuit operation.

EXAMPLE 3 A 1968 Dodge automobile equipped with a standard 4 cycle,internal combustion engine was selected for testing. The engine wastested in a manner similar to that of Example 1. The engine exhaust gascarbon monoxide concentration at 2500 rpm. was 1.0% by volume, while thecarbon monoxide concentration at idle was 5.5% by volume. The exhaustgas hydrocarbon concentration was 1200 ppm. at 2500 rpm. and 350 ppm. atidle. These data indicated that the engine had a malfunction resultingin improper fuel combustion.

The engine ignition system was inspected and it was found that the sparkplugs were worn and fouled. Replacement of these spark plugs resulted ina reduction in exhaust gas hydrocarbon concentration of 79% at 2500 rpm.and about 6% at idle.

EXAMPLE 4 A 1966 Ford automobile equipped with a standard 4 cycle,internal combustion engine was selected for testing. The procedurefollowed was similar to that of Example l. The exhaust gas carbonmonoxide concentration at 2500 rpm. was 0.95% by volume and at idle as1.7% by volume. The exhaust gas hydrocarbon concentration was 1500 ppm.at 2500 rpm. and 700 ppm. at idle. These results indicated an enginemalfunction resulting in improper fuel combustion. The ignition systemwas inspected and it was found that the distributor rotor and cap wereworn and needed replacement. The replacement of these componentsresulted in an exhaust gas hydrocarbon concentration reduction of at2500 rpm. and 20% at idle.

EXAMPLE 5 A 1966 Plymouth automobile equipped with a standard 4 cycle,internal combustion engine was tested in a manner similar to that ofExample 1. The concentration of carbon monoxide in the engine exhaustgases was considered to be normal at both engine speeds, while theexhaust gas hydrocarbon concentration at 2500 rpm. was 820 ppm. and atidle was 320 ppm. These results indicated a malfunction resulting inimproper fuel combustion. The ignition system was inspected and it wasdetermined that a single spark plug was cracked and, therefore, neededreplacement. Replacing this single spark plug resulted in a reduction inhydrocarbon concentration at 2500 rpm. of 88% and at idle of 44%.

ln each of the preceeding examples, correction of the malfunctionindicated by practicing the present invention resulted in a substantialreduction in the amount of carbon monoxide or hydrocarbons emitted tothe atmosphere. Because of the concern over air pollution, this benefitof the present invention is increasingly important and, from thepoint-of-view of the public at large, may be the primary advantage ofthe present invention.

These examples illustrate that the present invention provides aninexpensive, highly portable and quick method for determining: (1)whether the internal combustion engine being tested does in fact have amal- 9 function which results in unnecessarily large emissions of carbonmonoxide and/or hydrocarbons; and (2) what the general nature of themalfunction is. Without this invention and in the absence of elaborateequipment, such as a chassis dynamometer, it would be necessary to taketime to test each individual engine component separately and, even then,the possibility would still exist that each component would befunctioning properly. This wasting of valuable maintenance time andskill can be avoided by practicing the present invention.

Example 2 is of particular significance, for this exam ple indicatesclearly that the method of the present invention is able to diagnose thepresence of malfunctions which result in unnecessarily highconcentrations of carbon monoxide and/or hydrocarbons without regard forthe absolute concentration of these components. The initial levels ofcarbon monoxide determined (i.e., 1.0% by volume at 2500 rpm. and 0.4%by volume at idle) are substantially below arbitrarily set acceptableemission standards which have been used in the past. This fact,notwithstanding, the method of the present invention pointed to amalfunction which upon being corrected resulted in asubstantial'reduction in the amount of carbon monoxide emitted to theatmosphere.

In summary, the preceeding examples illustrate that the method of thepresent invention is quick, uncomplicated and does not require a greatdeal of mechanical skill or experience to practice. The fact that duringthe practice of the invention, the engine is operated at no loadconditions and portable infra-red analyzers and tachometers can be used,makes this method extremely valuable for inexpensive testing of largenumbers of internal combustion engines. The portable, infra-redanalyzers and other equipment, such as oxygen analyzers, which may benecessary, can be loaded onto a truck or van which is sent from place toplace testing engines. This mobility feature is an additionaloutstanding benefit of the present invention.

While this invention has been described with respect to various specificexamples and embodiments, it is to be understood that the invention isnot limited thereto and that it can be variously practiced within thescope of the following claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A method for diagnosing malfunctions of internal combustion engineswhich result in exhaust gases having unnecessarily high concentrationsof carbon monoxide and hydrocarbons comprising:

1. analyzing for the carbon monoxide and hydrocarbon concentrations ofthe exhaust gases from said engine, said gases being sampled while saidengine is being operated in modes (A) and (B). said engine operationalmodes being at essentially constant no load conditions at normaloperating temperatures and (A) on the idle carburetion circuit and (B)on the main carburetion circuit, the engine being operated in modes (A)and (B) in any chronological sequence; and

2. comparing said carbon monoxide and hydrocarbon concentrations,wherein engine malfunctions resulting in an overly-rich air-fuel mixtureto said engine are indicated when the carbon monoxide concentrationobtained from operational mode (B) exceeds that from operational mode(A) and engine malfunctions resulting in improper fuel combustion areindicated when the hydrocarbon concentration obtained from operationalmode (B) exceeds that from operational mode (A); and

3. correcting at least one of said indicated engine malfunctions andthereby reducing at least one of said carbon monoxide and hydrocarbonconcentrations in said engine exhaust gases.

2. The method of claim'l, wherein said engine operated on the maincarburetion circuit is operated at a speed of at least about 1200 rpm.

3. The method of claim 2, wherein said carbon monoxide and hydrocarbonconcentrations are obtained by means of infra-red spectrometry.

4. The method of claim 1, wherein said engine operated on the maincarburetion circuit is operated at a speed from about 1,200 rpm. toabout 4,000 rpm.

5. The method of claim 4, wherein said carbon monoxide and hydrocarbonconcentrations are obtained by means of infra-red spectrometry.

6. The method of claim 5, wherein said engine is operated in associationwith a motor vehicle and the exhaust gases for analysis are sampled fromthe exhaust system effluent.

7. The method ofclaim 1, wherein said engine operated on the maincarburetion circuit is operated at a speed from about 2,000 rpm. toabout 3,000 rpm.

8. The method of claim 7, wherein said carbon monoxide and hydrocarbonconcentrations are obtained by means of infra-red spectrometry.

9. The method ofclaim 8, wherein said engine is operated in associationwith a motor vehicle and the exhaust gases for analysis are sampled fromthe exhaust system effluent.

10. The method of claim 1, wherein said carbon monoxide and hydrocarbonconcentrations are obtained by means of infra-red spectrometry.

1. A method for diagnosing malfunctions of internal combustion engineswhich result in exhaust gases having unnecessarily high concentrationsof carbon monoxide and hydrocarbons comprising:
 1. analyzing for thecarbon monoxide and hydrocarbon concentrations of the exhaust gases fromsaid engine, said gases being sampled while said engine is beingoperated in modes (A) and (B), said engine operational modes being atessentially constant no load conditions at normal operating temperaturesand (A) on the idle carburetion circuit and (B) on the main carburetioncircuit, the engine being operated in modes (A) and (B) in anychronological sequence; and
 2. comparing said carbon monoxide andhydrocarbon concentrations, wherein engine malfunctions resulting in anoverly-rich air-fuel mixture to said engine are indicated when thecarbon monoxide concentration obtained from operational mode (B) exceedsthat from operational mode (A) and engine malfunctions resulting inimproper fuel combustion are indicated when the hydrocarbonconcentration obtained from operational mode (B) exceeds that fromoperational mode (A); and
 3. correcting at least one of said indicatedengine malfunctions and thereby reducing at least one of said carbonmonoxide and hydrocarbon concentrations in said engine exhaust gases. 2.comparing said carbon monoxide and hydrocarbon concentrations, whereinengine malfunctions resulting in an overly-rich air-fuel mixture to saidengine are indicated when the carbon monoxide concentration obtainedfrom operational mode (B) exceeds that from operational mode (A) andengine malfunctions resulting in improper fuel combustion are indicatedwhen the hydrocarbon concentration obtained from operational mode (B)exceeds that from operational mode (A); and
 2. The method of claim 1,wherein said engine operated on the main carburetion circuit is operatedat a speed of at least about 1200 rpm.
 3. The method of claim 2, whereinsaid carbon monoxide and hydrocarbon concentrations are obtained bymeans of infra-red spectrometry.
 3. correcting at least one of saidindicated engine malfunctions and thereby reducing at least one of saidcarbon monoxide and hydrocarbon concentrations in said engine exhaustgases.
 4. The method of claim 1, wherein said engine operated on themain carburetion circuit is operated at a speed from about 1,200 rpm. toabout 4,000 rpm.
 5. The method of claim 4, wherein said carbon monoxideand hydrocarbon concentrations are obtained by means of infra-redspectrometry.
 6. The method of claim 5, wherein said engine is operatedin association with a motor vehicle and the exhaust gases for analysisare sampled from the exhaust system effluent.
 7. The method of claim 1,wherein said engine operated on the main carburetion circuit is operatedat a speed from about 2,000 rpm. to about 3,000 rpm.
 8. The method ofclaim 7, wherein said carbon monoxide and hydrocarbon concentrations areobtained by means of infra-red spectrometry.
 9. The method of claim 8,wherein said engine is operated in association with a motor vehicle andthe exhaust gases for analysis are sampled from the exhaust systemeffluent.
 10. The method of claim 1, wherein said carbon monoxide andhydrocarbon concentrations are obtained by means of infra-redspectrometry.